Special training was a very common thing for investigators.
As investigators, they often needed to survive in very harsh environments. Most of their talents were average, which made it so that they and their pets would often be two extremes in terms of combat strength. Once a battle broke out, the investigators themselves would become a huge breakthrough point.
If the investigator was too weak, they would be a burden.
As such, they often needed special training. It might not make one stronger, but at least one wouldn't be a burden in battle.
Putting everything else aside, one had to at least be able to run, right?
The special training of the Investigation Corps was especially strict. Pets weren't allowed.
After all, once the pets could be brought along, the special training would be meaningless.